Gravity tidings from domain walls: Flavour hierarchies are making waves

TL;DR

This paper explores how domain walls from spontaneously broken discrete flavour symmetries in particle physics models can produce observable gravitational waves, linking fermion mass hierarchies to cosmological signals.

Contribution

It analyzes minimal supersymmetric and non-supersymmetric models where gravity-induced domain walls generate gravitational waves, providing potential observational signatures.

Findings

Domain walls can produce detectable gravitational wave backgrounds.

Gravity effects can lift vacuum degeneracy, leading to wall annihilation before nucleosynthesis.

Models predict characteristic gravitational wave signals linked to flavour symmetry breaking.

Abstract

Explaining the observed charged fermion mass hierarchies points to flavour symmetries inducing a suppression of the lighter species' masses. When the symmetries are global, it is expected that such symmetries are broken by gravity via Planck scale suppressed effective operators. The potential of the spontaneous symmetry-breaking "flavon" field, if the symmetry is discrete, then possesses several minima, with the vacuum-degeneracy lifted by the gravity effects. In such scenarios, domain walls might be generated in the process of symmetry breaking. Due to the bias, however, they potentially annihilate sufficiently before Big Bang nucleosynthesis, avoiding conflict with observations and generating a characteristic contribution to the stochastic gravitational wave background. We discuss whether and how minimalistic supersymmetric and non-supersymmetric realisations of such theories can give rise to observable gravitational waves.